Re: [PATCH next] audit: fix potential double free on error path from fsnotify_add_inode_mark

On Mon 22-08-22 10:34:15, Paul Moore wrote: > On Mon, Aug 22, 2022 at 4:50 AM Jan Kara <jack(a)suse.cz&gt; wrote: > > On Mon 22-08-22 10:29:05, Gaosheng Cui wrote: > > > Audit_alloc_mark() assign pathname to audit_mark->path, on error path > > > from fsnotify_add_inode_mark(), fsnotify_put_mark will free memory > > > of audit_mark->path, but the caller of audit_alloc_mark will free > > > the pathname again, so there will be double free problem. > > > > > > Fix this by resetting audit_mark->path to NULL pointer on error path > > > from fsnotify_add_inode_mark(). > > > > > > Fixes: 7b1293234084d ("fsnotify: Add group pointer in fsnotify_init_mark()") > > > Signed-off-by: Gaosheng Cui <cuigaosheng1(a)huawei.com&gt; > > > > Good spotting! The patch looks good to me. Feel free to add: > > > > Reviewed-by: Jan Kara <jack(a)suse.cz&gt; > > > > > --- > > > kernel/audit_fsnotify.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/kernel/audit_fsnotify.c b/kernel/audit_fsnotify.c > > > index 6432a37ac1c9..c565fbf66ac8 100644 > > > --- a/kernel/audit_fsnotify.c > > > +++ b/kernel/audit_fsnotify.c > > > @@ -102,6 +102,7 @@ struct audit_fsnotify_mark *audit_alloc_mark(struct audit_krule *krule, char *pa > > > > > > ret = fsnotify_add_inode_mark(&audit_mark->mark, inode, 0); > > > if (ret < 0) { > > > + audit_mark->path = NULL; > > > fsnotify_put_mark(&audit_mark->mark); > > As I'm tracing the code path from audit through fsnotify, and back > into audit, I'm wondering if we still have a problem. When > fsnotify_add_inode_mark() fails it will end up freeing not just > audit_mark->path, but audit_mark itself via audit_fsnotify_mark_free() > (via a call into fsnotify_put_mark()), yes? I don't think so. fsnotify_add_mark_locked() will call fsnotify_put_mark() but that is just a counter part to fsnotify_get_mark() a few lines above. The caller of fsnotify_add_inode_mark() still holds its own mark reference which prevents mark from being freed.